Wide area ablation of myocardial tissue

ABSTRACT

The present invention advantageously provides a method and system for cryogenically ablating large areas of tissue within the left atrium. In an exemplary embodiment a cryotherapy device includes a catheter body having a substantially fixed diameter, a proximal end and a distal end; a first lumen for permitting passage of a cooling fluid from the proximal end to the distal end; a second lumen permitting return of the cooling fluid from the distal end to the proximal end; and an ablation element expandable from a first diameter that is substantially the same as the diameter of the catheter body to a second diameter that is at least twice the diameter of the catheter body, the ablation element having a surface portion that conforms to the uneven surface topography of the cardiac tissue. The ablation element can include one or more balloon and/or a flexible element that is deformed by moving the distal end of the catheter toward the proximal end of the catheter. The surface of the balloon can further be shaped by regulation of pressure within the one or more balloons. In an exemplary method a tissue ablation device is provided and tissue in the antrum of the left atrium is ablated with the device. In an exemplary method, only tissue in the antrum is ablated, and the ablation is created by freezing tissue.

CROSS-REFERENCED TO RELATED APPLICATION

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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FIELD OF THE INVENTION

The present invention relates to a method and system for interventionalelectrophysiology and minimally invasive cardiovascular surgery.

BACKGROUND OF THE INVENTION

Minimally invasive surgical techniques are known for performing medicalprocedures within all parts of the cardio-vascular system. Exemplaryknown procedures include the steps of passing a small diameter,highly-flexible catheter through one or more blood vessels and into theheart. When positioned as desired, additional features of the catheterare used, in conjunction with associated equipment, to perform all or aportion of a medical treatment, such as vessel occlusion, tissue biopsy,or tissue ablation, among others. Almost always, these procedures areperformed while the heart is beating and blood is flowing. Notsurprisingly, even though visualization and positioning aids areadequate for general placement of the device, maintaining the device ina selected position and orientation can be difficult as the tissue movesand blood flows, especially during a procedure that must be donequickly. As diagnostic and visualization equipment and techniques havecontinued to evolve, it has become possible to identify tissue areas tobe treated with greater precision than the ability to quickly situatethe device and effectuate treatment.

In addition to the challenges presented by moving tissue and flowingblood, the actual topography of the tissue being treated presentschallenges. For example, unlike stylized drawings that depict theinterior of the chambers of the heart as having smooth, evenly curvedwalls leading neatly to tubular blood vessels, the interior surfaces ofthe heart's chambers are irregular, uneven, and fibrous, as are theopenings to blood vessels. Thus, for procedures that call for uniformtissue contact or tissue contact along an extended line, the structureand techniques for use of known devices can be deficient in someregards.

Even if a device is capable of being properly placed and held inposition at the proper orientation; and even if the device is suitablefor the tissue topography at the treatment site, the device can benevertheless not fully suitable to achieve the desired outcome. By wayof example, catheter-based devices are known for placement in the leftatrium for ablating tissue within the atrium for the purpose ofelectrically isolating one or more pulmonary veins from the atrium in anattempt to increase the success rate of atrial fibrillation ablation.

In one type of prior art device disclosed in U.S. Patent Publication2002/012836 A 1, and as shown in FIG. 1 (prior art), a sheath or guidecatheter 10 is inserted into a blood vessel 12 that leads to the rightatrium 14 of the heart 16 and passed through an opening created in theseptum 18 that separates the right and left atria into the left atrium20. As shown in FIG. 2 (prior art), a treatment element 22 is passedthrough the guide catheter 10, deployed from an opening in the distalend thereof and caused to form a substantially circular loop that istraverse or perpendicular to the longitudinal axis of the guide catheter10. A distal tip element 24 that extends distally beyond the circularloop is inserted into a pulmonary vein 26 as a guide and placement aidfor the loop. As shown in FIG. 3 (prior art), the treatment element 22in the form of a loop is placed so that it encircles the opening orentry of the pulmonary vein 26, known as the ostium and tissue isablated by microwave heating of the contacted tissue. The intendedresult is a substantially uniform circle of ablated tissue 28 as shownin FIG. 4 (prior art). Also as shown in FIG. 4 (prior art), such adevice can be used in an attempt to create linear lesions 30 and 32 aswell.

In practice, uniform, unbroken lesion lines are hard to create with suchloop shaped ablation elements. Also, with respect to both the circularand the linear lesions formed by microwave ablation, it should be notedthat the lesion formed is relatively narrow and has a width thatcorresponds to about the width of the catheter. Devices that use a laserto ablate tissue provide a similar result; namely, a very narrow lesion.Further, because a laser ablates a very narrow line of tissue, precisealignment of the device is very important. However, for the reasons setforth above, such precision is very difficult to achieve.

In another type of device disclosed in U.S. Pat. No. 6,164,283 electrodeelements, capable of ablating tissue when energized, arecircumferentially disposed on the exterior of a balloon element that isplaced at least partially within a pulmonary vein, so that theelectrodes are positioned to form a circumferential conduction blockalong a circumferential region of tissue in a pulmonary vein wall. Otherdevice configurations are disclosed that have an electrode bandpositioned on an expandable member for ablating a circumferential patharound the ostium and tissue along the posterior atrial wall whichsurrounds the pulmonary vein.

Recently, companies such as CryoCath Technologies Inc., Montreal,Canada, have developed catheter based devices that cryogenically ablatetissue. These devices are structurally very different from RF catheterbased devices, and they are not similar or comparable variations on thesame theme. Not only are the structures that encompass the respectiveablation technologies different, but so are the devices for controllingthe ablation process, evaluating the progress and extent of ablation,and ensuring patient safety.

For example, to create a large “ring” with and RF catheter it isnecessary to make a series of adjoining spot lesions of relatively smallsize using small electrode if one wishes to minimize RF output. This issignificant because use of a large electrode and/or high power outputcan seriously injure tissue at other than the intended treatment site.This is especially important with respect to creating lesions in thepulmonary veins because the veins are juxtaposed with bronchial tubesand other sensitive pulmonary tissue within which it is highlyundesirable to create ancillary lesions. By contrast, cryogenic ablationof tissues does not need to be accomplished “bit by bit” for fear totransmission of energy into tissue and the transfer of heat occurs atthe medical device.

Another disadvantage common to RF and other non-cryogenic devices thatwas identified above is the difficulty of maintaining such a device in aselected position while the heart is beating. By contrast, a cryogenicdevice does not have this problem because the subfreezing temperaturescreated by the device causes the device to firmly stick or adhere totissue at a treatment site. Still further, RF energy causes cellulardeath and side effects that are specific to the use of RF energy andthat contrast considerably with the effects of cooling and the cellulardeath caused by freezing tissue.

Thus, although RF ablation may be appropriate and safe for tissueablation in other areas of the body, clinical studies have revealed thatcreating of RF lesions in the pulmonary veins does not appearadvantageous for the reasons set forth above. Further, RF ablation ofthe pulmonary veins has been associated with left atrial-esophagealfistula, pulmonary vein stenosis, tamponade, and significant radiationexposure. Therefore, if a cryogenic device were available as analternative to RF ablation devices and techniques for the treatment ofatrial fibrillation, it would be preferable to use the cryogenic deviceto avoid the problems created by the use of RF energy.

Notwithstanding the apparent advantages of cryoablation over other typesof ablation, particularly RF, with respect to treatment of atrialfibrillation, very few cryoablation devices have been conceived for thispurpose. Or, if cryoablation has been considered, it is mentioned as ifit were synonymous with RF ablation, with no actual thought ordisclosure provided that is enabling for such a structurally dissimilardevice or that takes into account the very different effects of the useof the respective devices on tissue. For example, although U.S. Pat. No.6,164,283 makes a brief, generalized reference to use of a cryoablationelement to cool tissue, no specific details are set forth with respectto such a device.

Only one known device addresses issues related to cryoablationtechnology with respect to an attempted treatment of atrialfibrillation. Specifically, a cryoballoon catheter provided by BostonScientific Corporation, Natick, Mass., has been used to createcryolesions by delivering liquid N₂O into a semi-compliant balloonpositioned at the pulmonary vein-left atrial interface. Thus, the devicehas basically been used as a substitute for an RF device to performsubstantially the same procedure that is set forth in U.S. Pat. No.6,164,283; namely, the creation of a substantially annular ring ofablated tissue at the ostium of the pulmonary vein. Although this devicemay obviate the adverse effects of the earlier RF devices it would bedesirable to provide a cryoablation device that more fully exploits theinherent advantages of a cryogenic ablation device.

SUMMARY OF THE INVENTION

The present invention advantageously provides a method and system forcryogenically ablating large areas of tissue within the left atrium.

In an exemplary embodiment a cryotherapy device is provided formodifying the electrophysiological properties of cardiac tissue havingan uneven surface topography, wherein the device includes a catheterbody having a substantially fixed diameter, a proximal end and a distalend; a first lumen for permitting passage of a cooling fluid from theproximal end to the distal end; a second lumen permitting return of thecooling fluid from the distal end to the proximal end; and an ablationelement expandable from a first diameter that is substantially the sameas the diameter of the catheter body to a second diameter that is atleast twice the diameter of the catheter body, the ablation elementhaving a surface portion that conforms to the uneven surface topographyof the cardiac tissue. The ablation element can include one or moreballoon and/or a flexible element that is deformed by moving the distalend of the catheter toward the proximal end of the catheter. The surfaceof the balloon can further be shaped by regulation of pressure withinthe one or more balloons.

The invention also include a method for modifying theelectrophysiological properties of cardiac tissue wherein a tissueablation device is provided and tissue in the antrum of the left atriumis ablated with the device. In an exemplary method, only tissue in theantrum is ablated, and the ablation is created by freezing tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 depicts a prior art technique for placing a distal portion of amedical device within the heart;

FIG. 2 illustrates a prior art technique for positioning a prior artdevice within the left atrium;

FIG. 3 depicts a prior at technique for creating a lesion with a priorart microwave ablation device;

FIG. 4 shows lesions formed using the prior art techniques and devicesof FIGS. 1, 2 and 3;

FIG. 5 is schematic illustration of a cryogenic ablation system inaccordance with the present invention;

FIG. 6 is a side view of an exemplary ablation element for the system ofFIG. 5;

FIG. 7 depicts the ablation element of FIG. 6 is an expanded state;

FIG. 8 shows an alternative embodiment of the ablation element of FIG.6, wherein a membrane is disposed over expansion elements positioned inan expanded state;

FIG. 9 is a front view of the ablation element of FIG. 6, wherein anablation pattern created by the device is shown;

FIG. 10 illustrates an alternative embodiment for the ablation elementin a partially expanded state;

FIG. 11 illustrates the ablation element of FIG. 10 in a fully expandedstate;

FIG. 12 depicts the ablation element of FIG. 10 in a partially inflatedstate suitable for deflection;

FIG. 13 depicts the ablation element of FIG. 10 in the partiallyinflated state shown in FIG. 12 being defected to a cured configuration;

FIG. 14 shows yet another embodiment of the ablation element;

FIGS. 15-17 illustrate the ablation element in exemplary deploymentconfigurations;

FIG. 18 illustrates yet another embodiment of an ablation element;

FIG. 19 shows the ablation element of FIG. 18 in a deflected condition;

FIG. 20 show yet another ablation element in accordance with theinvention; and

FIG. 21 illustrates an ablation device in accordance with the inventionwithin the left atrium of the heart having created lesions in the leftantral region.

DETAILED DESCRIPTION OF THE INVENTION

With respect to the treatment of atrial fibrillation, it is believedthat the creation of a conduction block or an interruption of theelectrical signal flow path from the region of the atrium and thepulmonary vein is an effective treatment for atrial fibrillation.Further, while it is believed that the creation of a narrow annularlesion at or very near the ostium of the pulmonary vein is an effectiveway to create a conduction block, notwithstanding the difficulty ofmaking such a lesion, it is believed that creating of one or morenon-annular lesions in different locations is not only more readilyaccomplished with reliability but it is more clinically effective.

In view of the preceding, the present invention provides apparatus andmethods for modifying the electrophysiological properties of large areasof tissue rather than narrow, annular lesions at locations that are notconfined solely to the ostium, although ablation of tissue near theostium and/or in the atrial wall may be included. More particularly, thepresent invention provides devices that are suitable to cryogenicallyablate regions of tissue in the antrum region of the left atrium inaddition to other atrial tissue that may be deemed to be arrhythmogenic.The antrum is the area between the mouth or ostium of a pulmonary veinand the atrium. The antrum of each pulmonary vein is not identical insize or shape and the tissue topography renders it very difficult oralmost impossible to create a ring of tissue. Accordingly, the presentmethod calls for ablating large regions of tissue in the antrum torender the tissue electrically dysfunctional.

Referring now to FIG. 5, an exemplary system is depicted that issuitable for performing cryogenic antral ablation. The system includesan elongate highly flexible ablation catheter 34 that is suitable forpassage through the vasculature. The ablation catheter 34 includes acatheter body 36 having a distal end 37 with an ablation element 38 ator proximal to the distal end. The distal end 37 and the ablationelement 38 are shown magnified and are described in greater detailbelow. The ablation catheter 34 has a proximal end 40 that is mated to ahandle 42 that can include an element such as a lever 44 or knob formanipulating the catheter body 36 and the ablation element 38. In theexemplary embodiment, a pull wire 46 having a proximal end and a distalend has its distal end is anchored to the catheter at or near the distalend 37. The proximal end of the pull wire is anchored to an element suchas a cam 48 in communication with and responsive to the lever 44. Thehandle 42 can further include circuitry 50 for identification and/or usein controlling of the ablation catheter or another component of thesystem.

Continuing to refer to FIG. 5, the handle 42 can also include connectorsthat are matable directly to a cryogenic fluid supply/exhaust andcontrol unit or indirectly by way of one or more umbilicals. In thesystem illustrated, the handle 42 is provided with a first connector 54that is matable with a co-axial fluid umbilical (not shown) and a secondconnector 56 that is matable with an electrical umbilical (not shown)that can further include an accessory box (not shown). In the exemplarysystem the fluid supply and exhaust, as well as various controlmechanisms for the system are housed in a single console 52. In additionto providing an exhaust function for the ablation catheter fluid supply,the console can also recover and/or recirculate the cooling fluid. Thehandle 42 is provided with a fitting 58 for receiving a guide wire (notshown) that is passed into a guide wire lumen 60.

Still referring to FIG. 5, the ablation element 38 is shown as a doubleballoon, wherein an inner balloon 62 is contained by an outer balloon64. A coolant supply tube 66 in fluid communication with the coolantsupply in the console 52 is provided to release coolant from one or moreopenings in the tube within the inner balloon 62 in response to consolecommands and other control input. A vacuum pump in the console 52creates a low pressure environment in one or more lumens within thecatheter body 36 so that coolant is drawn into the lumen(s), away fromthe inner balloon, and toward the proximal end of the catheter body. Thevacuum pump is also in fluid communication with the interface of theinner and the outer balloons so that any fluid that leaks from the innerballoon is contained and aspirated. Still referring to FIG. 5, thehandle includes one or more pressure sensors 68 to monitor the fluidpressure within one or both of the balloons, blood detection devices 70and pressure relief valves 72. When coolant is released into the innerballoon 62, the inner and the outer balloon 64 expand to a predeterminedshape to present an ablation surface, wherein the temperature of theablation surface is determined by the material properties of thespecific coolant selected for use, such as nitrous oxide, along with thepressure within the inner balloon and the coolant flow rate.

Although the double balloon type ablation element 38 illustrated in FIG.5 can be an effective ablation tool, FIGS. 6-20 illustrate otherconfigurations for the ablation element that are capable of creatingwide-area ablation patterns. For example, as shown in FIG. 6, a distalcatheter portion 74 includes longitudinal elements 76 secured to a maincatheter body 78 proximally, and to a tip element 80, distally. A pullwire 82 or pushrod connected to a manipulation element 44 at theproximal end of the catheter and to the tip element 80 is movablelongitudinally to move the tip element longitudinally. Electrodes 84 canbe associated with one or more of the longitudinal elements for use inmonitoring or evaluating electrical activity in tissue.

As shown in FIG. 7, the pull wire 82 has been pulled proximally to drawthe tip element 80 toward the catheter body 78. This causes thelongitudinal elements 76 to deform and bend or bow radially outward. Inone embodiment, each of the longitudinal elements 76 are provided withcoolant injection tubes 83 disposed within a lumen defined by eachlongitudinal element, wherein coolant is recovered in the lumen which isin fluid communication with a low pressure source. Thus, each of thelongitudinal elements 76 are cooled. Although the injection tubes 83 canall be supplied with coolant simultaneously, if desired, less than allof the injection tubes can be supplied with coolant to provideselectively radial cooling.

As shown in FIG. 8, the longitudinal elements can support a single or adouble layer flexible member 85 that envelops them. Instead of, or inaddition to coolant being circulated through the longitudinal members asdiscussed with respect to FIG. 7, coolant can be circulated through thechamber defined by the elements and the flexible member as describedwith respect to FIG. 5 and the pull wire 82 can be used to deform theballoon by moving the distal end of the device proximally and distally.

FIG. 9 is a front view of the device of FIGS. 7 and 8 and it illustratesthe general shape of the periphery 86 of a lesion formed by cryoablationusing the exemplary device in the expanded state. By contrast, spot orlinear lesions can be created when the distal catheter portion 74 is inthe non-expanded state illustrated in FIG. 6.

Referring now to FIG. 10, a catheter is provided with an ablationelement 88 similar to the double balloon structure of FIG. 5 so that adistal tip region 90 is radially expandable to at least double thediameter of a catheter body 92 over a 2 cm to 3 cm length. The ablationelement 88 is provided with a cryogenic fluid injection tube 94 havingone or more fluid outlets 96 along its length in the distal tip region.Coolant is withdrawn though an outer lumen 98 at reduced pressure. Apull wire 100 or pushrod is used to deflect the distal catheter portionas shown in FIG. 11 so that a large, distal facing surface 102 can beplaced into contact with tissues. Although the balloon when inflated asshown in FIG. 10 has a substantially greater radius than the catheterbody 92, when the pull wire 100 is used to draw the distal tip towardthe catheter body as shown in FIG. 11, the balloon expands even furtherand presents a flattened tip that is suitable to blot large areas oftissue.

Referring now to FIG. 12, an ablation element 104 is provided with adistal portion 106 that is inflatable, one or more coolant injectionorifices 108 and an exhaust lumen 110. Referring to FIG. 13, theablation element 104 is shown with a pull wire 111 or pushrod connectedto a manipulation element at the proximal end of the catheter and thetip element 12 so as to be movable longitudinally to deflect the tipelement off axis. In addition to providing a relatively long and wideablation surface, the ablation element can be provided with a notch 114to accommodate or fit over a ridge of tissue.

FIGS. 14-17 illustrate an embodiment for an ablation element, whereinfirst and second balloons, 116 and 118, respectively, are enveloped by athird balloon 120. The first and the second balloons 116 and 118 are influid communication with inflation and exhaust lumens as describedabove, wherein the third balloon 120 is only in communication with avacuum or low pressure source. Each of the first and second balloons isprovided with a shape and/or is pressurized to provide an overallsurface topography for the ablation element. Additional shaping isprovided by manipulation of a pull wire as described above or byregulation of the pressure in the exhaust flow path.

Referring now to FIGS. 18 and 19, yet another configuration for anablation element is shown wherein an ablation element includes anelastically deformable, thermally-transmissive tip element 122 securedto the distal portion of a catheter body 124. When a load is applied tothe tip element 122 it deforms. For examples, FIG. 19 illustrates thetip element subject to an axial load, such as is encountered when thetip is pressed against tissues. As shown, the distal portion of the tipelement 122 presents a wider ablation surface when deflected as comparedto the non deflected states. When the load is removed from the tip, itreturns to the shape illustrated in FIG. 18. Fluid supply and exhaustlumens are provided as disclosed above. Also as described above, a pullwire 125 can be secured to the tip element 122 to help deform theelement so that it doesn't need to be pressed hard against tissue. In anexemplary embodiment the tip element 122 is configured so that it isbiased into the shape illustrated in FIG. 18. Proximal tension isapplied to the pull wire 125 to deform or aid in deforming the tipelement to an expanded configuration as shown in FIG. 19. Whenproximally directed tension is reduced on the pull wire 125, the biasingforce of the tip element causes it to return to the configuration shownin FIG. 18.

FIG. 20 illustrates yet another configuration of an ablation elementwherein a catheter body 126 has a distal end 128 covered with a mass ofthermally conductive, highly elastic material, such as a cohesive gel130. When the distal end 128 and the gel 130 are pressed against tissue,the gel deforms to provide an enlarged distal end portion as shown bythe dashed line 132. Coolant exiting a coolant supply tube 134 cools thedistal end 128 and the gel 130.

Turning now to FIG. 21, an exemplary procedure is illustrated wherein anablation element 136 in accordance with the invention has been deliveredtranseptally into the left atrium using known techniques. In theillustration, the ablation element 136 is a balloon that is partiallyinflated with a nitrous oxide coolant so that it has a “squishy” orhighly compliant character and dimensioned so that it can “blot” orcontact an area of tissue approximately 28 to 30 mm in diameter. In theexemplary procedure, the balloon is inflated to the desired degree offirmness, or lack thereof, before being advanced toward tissue and theballoon's surface is chilled to a temperature in the range of minus 30degrees Centigrade to minus 80 degrees Centigrade. The balloon is thenplaced into contact with tissue in the antrum 138 and the tissue isablated. The balloon is moved to one or more additional areas of theantrum 138 until the desired tissue modification has been achieved. Theballoon can be placed so as to created individual distinct lesions oroverlapping lesions. In this fashion, large contiguous lesions can becreated. The pattern 139 shown in FIG. 21 illustrates an exemplarylesion periphery created with the ablation element 136.

Because the doctor is not attempting to create a “ring,” the balloondoes not have to be centered on the ostium 140 and no anchoring isneeded. In general, for any of the disclosed cryoablation devices,precise alignment is not as important as with respect to other devices.This is significant, because the precise positioning within the antrumis difficult to achieve. The balloon does not enter the pulmonary vein142. However, depending upon placement of the balloon, the temperatureachieved, and the duration that the balloon is left in place, ispossible to ablate tissue in the ostium 140 in addition to tissue withinthe pulmonary vein 142, as well as the antrum 138.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing front the scope andspirit of the invention, which is limited only by the following claims.

1-20. (canceled)
 21. A cryotherapy device for treating cardiac tissue,comprising: a catheter body defining a proximal end and a distal end;and a thermally conductive gel disposed on the distal end of thecatheter body.
 22. The cryotherapy device of claim 21, wherein the gelis deformable upon contact with the cardiac tissue.
 23. The cryotherapydevice of claim 21, wherein the catheter body defines a fluid flow paththerethrough.
 24. The cryotherapy device of claim 23, further comprisinga cryogenic fluid supply in fluid communication with the fluid flow pathof the catheter body.
 25. The cryotherapy device of claim 24, furthercomprising a vacuum pump in fluid communication with the fluid flow pathof the catheter body.
 26. The cryotherapy device of claim 23, furthercomprising a pressure sensor in fluid communication with the fluid flowpath of the catheter body.
 27. The cryotherapy device of claim 21,further comprising a pull wire at least partially disposed within thecatheter body.
 28. A cryotherapy device for treating cardiac tissue,comprising: a catheter body defining a proximal end, a distal end, and afluid flow path therethrough; a thermally conductive, deformable geldisposed on the distal end of the catheter body in thermal communicationwith the fluid flow path; and a cryogenic fluid supply in fluidcommunication with the fluid flow path.
 29. The cryotherapy device ofclaim 28, further comprising a vacuum pump in fluid communication withthe fluid flow path of the catheter body.
 30. The cryotherapy device ofclaim 28, further comprising a pressure sensor in fluid communicationwith the fluid flow path of the catheter body.
 31. The cryotherapydevice of claim 28, further comprising a pull wire at least partiallydisposed within the catheter body.
 32. A method for modifying theelectrophysiological properties of cardiac tissue, comprising: deformingat least a portion of a treatment element upon contact with an uneventopography of cardiac tissue; and ablating the cardiac tissue at leastin part by cooling the treatment element.
 33. The method of claim 32,wherein cooling of the treatment element includes circulating acryogenic fluid into thermal contact with the treatment element.
 34. Themethod of claim 33, further comprising evacuating the cryogenic fluidfrom thermal contact with the treatment element.
 35. The method of claim32, further comprising maintaining the deformation of the treatmentelement during ablation.
 36. The method of claim 32, further comprisingat least partially obstructing an orifice in the cardiac tissue with thetreatment element.
 37. The method of claim 32, wherein the treatmentelement includes a partially inflated balloon.
 38. The method of claim32, wherein the treatment element includes a thermally-conductive gel.